SMTP Server offline

My VPS provider got DDOS'ed last week, after they have fixed this and my VPS got back online the SMTP Server doesnt work anymore.
Now i have looked on many places to find the problem but i cant find the problem anywhere.

main.cf:

# See /usr/share/postfix/main.cf.dist for a commented, more complete version

# Debian specific: Specifying a file name will cause the first
# line of that file to be used as the name. The Debian default
# is /etc/mailname.
#myorigin = /etc/mailname

smtpd_banner = $myhostname ESMTP $mail_name (Debian/GNU)
biff = no

# appending .domain is the MUA's job.
append_dot_mydomain = no

# Uncomment the next line to generate "delayed mail" warnings
#delay_warning_time = 4h

After testing whole of things again sended mails from my hotmail to my mail and when i start the postfix just after i sended the mail from my hotmail it delivers sometimes to my mail but after a few seconds the SMTP Server is offline again.